The present invention, in some embodiments thereof, relates to peptides and, more particularly, but not exclusively, to uses thereof in inhibiting Insulin-Degrading Enzymes (IDE).
Diabetes is a syndrome characterized by disordered metabolism and abnormally high blood sugar (hyperglycemia) resulting from insufficient levels of the hormone insulin. The most common forms of diabetes are Diabetes mellitus type 1, Diabetes mellitus type 2 and gestational diabetes. Diabetes is usually associated with excessive urine production, resulting compensatory thirst and increased fluid intake, blurred vision, unexplained weight loss, lethargy and changes in energy metabolism.
All types of diabetes have been treatable since insulin became medically available in 1921. Patients with Diabetes mellitus type 1 depend on external insulin (most commonly injected subcutaneously) as the hormone is no longer produced by their pancreas (by the islets of Langerhans). Patients with Diabetes mellitus type 2 or gestational diabetes are typically insulin resistant and may require insulin to control blood glucose levels [Vinik et al. (2004) MedGenMed 6:12].
In normal individuals (i.e. non-diabetics) increased insulin levels lead to glucose absorption and storage in cells, consequently reducing glycogen to glucose conversion, reducing blood glucose levels, and thereby reducing insulin release. Therefore, normally the blood glucose level rises somewhat after eating and within an hour or so returns to the normal ‘fasting’ level. When treating a patient with insulin (e.g. synthetic human insulin or insulin analogs) the right dose and the right timing of administration must be determined and achieving physiological regulation of blood glucose, as in non-diabetics, is attempted. However, treatment of diabetic patients with insulin usually falls far short of normal glucose control and maintaining the basal rate and the bolus rate is a continuous balancing act that patients with insulin-dependent diabetes must manage on a daily basis [Vinik et al., supra]. Moreover, there is often a reluctance on the part of many care providers to prescribe insulin due to fear of weight gain, hypoglycemia, cardiovascular consequences or because the patient is unwilling to co-operate. Furthermore, continuous injection of insulin increases the risk of insulin binding to antibodies that appear to be a strong risk factor for inexplicable severe hypoglycemia in patients with Diabetes mellitus type 1.
Insulin is critical for glucose, lipid, and protein metabolism as well as for cell growth and differentiation. It is cleared from the body mainly by the liver and kidney, but most other tissues also degrade insulin. Insulin-degrading enzyme (IDE, insulysin) is the major enzyme responsible for insulin degradation [Simkin et al. (1949) Arch Biochem 24:422-428]. IDE is an approximately 110 kDa thiol zinc-metalloendopeptidase located in cytosol, peroxisomes, endosomes, and on the cell surface. This enzyme cleaves small proteins of diverse sequences many of which share a propensity to form β-pleated sheet-rich amyloid fibrils, including amyloid β-protein (Aβ), insulin, glucagon, amylin, atrial natriuretic factor and calcitonin [Simkin et al., supra].
The IDE region of chromosome 10q has been genetically linked to type 2 diabetes mellitus [DM2, Ghosh et al. (2000) Am J Hum Genet 67:1174-1185; Wiltshire et al. (2002) Am J Hum Genet 70:543-546] and to elevated fasting glucose levels [Meigs et al. (2002) Diabetes 51:833-840]. Moreover, IDE−/− mice had hyperinsulinemia and glucose intolerance, hallmarks of DM2 [Farris et al. (2003) Proc Natl Acad Sci USA 100:4162-4167]. This model demonstrated that in vivo deficiency of a protease responsible for degrading insulin results in hyperglycemia in response to a glucose load (i.e., glucose intolerance).
Reports have further suggested the role of IDE in degradation of Aβ in Alzheimer's disease [Farris et al., supra]. The elevation of cerebral Aβ in IDE−/− model animals (approximately 10-65%) validated a role for IDE in Aβ proteolysis in vivo, however, there are most likely additional mechanisms of Aβ clearance in the intact brain, especially for Aβ42. Other proteases (e.g., NEP, endothelin-converting enzyme) may participate in Aβ clearance and partially compensate for the lack of IDE function.
IDE is also the cellular receptor mediating varicella-zoster virus (VZV) infection and cell-to-cell spreading [Li et al. (2006) Cell 127:305-316]. Down regulation of IDE by siRNA, or blocking IDE with an antibody, with a soluble IDE protein (extracted from the liver) or with a bacitracin inhibited VZV infection [Li et al., supra]. IDE interacts with glycoprotein E (gE), which is essential for virus infection, through the glycoprotein's extracellular domain, however, IDE does not degrade VZV.
The solved crystal structure of IDE [Shen et al. (2006) Nature 443:870-874] revealed that the amino- and carboxy-terminal domains of IDE (IDE-N and IDE-C, respectively) form a proteolytic chamber containing the zinc-binding active site, just large enough to encapsulate insulin. Extensive contacts between IDE-N and IDE-C keep the degradation chamber of IDE inaccessible to substrates. Repositioning of the IDE domains (shifting IDE-close to its active form IDE-open) enables substrate access to the catalytic cavity (FIG. 1). The activity of IDE toward a vast array of physiological substrates can be partially explained by the detailed crystal structure of the enzyme. The structural data revealed that IDE is shaped like a clam shell, consisting of two bowl-shaped halves connected by a flexible hinge, which allows the enzyme to exist in two conformations, closed and open. During catalytic processing of substrates, the enzyme switches from the open structure to the closed configuration and back to the open structure as IDE binds, catalyzes, and then releases its substrate, respectively. The extended hydrogen bonding between the two halves of IDE creates a “latch” that acts to maintain the enzyme in the closed state. Mutations that promote the open conformation have been shown to improve the protease's efficiency in cleaving the substrate by as much as 30- to 40-fold [Shen et al., supra]. As it was suggested that the rate-limiting step may be the speed at which the enzyme can reopen and then clamp down on a new morsel rather than the time it takes to chew something up.
U.S. Pat. Appl. No. 20030104981 discloses novel human insulin analogues for treating Diabetes Mellitus, the analogues being characterized by having enhanced stability to insulin-degrading enzyme (IDE) as well as achieving longer life times than native insulin. The insulin analogues taught by U.S. Pat. Appl. No. 20030104981 were characterized structurally by elimination of B26-B30 in the human insulin B-chain and by having at least one specified substitution at B10, B14 and B17.
U.S. Pat. No. 7,108,972 discloses polynucleotides and polypeptides and uses of same, including two NOV3 nucleic acid sequences encoding Insulysin-like proteins. According to U.S. Pat. No. 7,108,972, these Insulysin-like proteins may be used in diagnosis and therapeutics of various diseases and disorders including diabetes.